Hierarchical Systems

Many astrophysical systems are arranged in hierarchical configurations. First, we considered the evolution of orbits of stars orbiting a supermassive black hole (SBH). Such nuclear star clusters are within the centers of most galaxies. We studied the long-term evolution and computed tidal disruption rates of stars by the SBH. Such disruption events reveal the physics and properties of stars and SBHs.

In related work, we studied the dynamics of planetesimals in the galactic center (GC). When planetesimals are tidally disrupted by the SBH, this can produce a potentially observable flare. We computed the rates of such disruptions, and found rates consistent with observations, suggesting that planetesimals are formed in the GC around stars, similarly to stars in the solar neighbourhood.

Subsequently, we considered the long-term evolution of hierarchical quadruple systems. We applied our techniques to provide an explanation for the lack of transiting circumbinary planets around short-period binaries.

Lastly, we generalised our methods, and applied them to study the implications of the long-term dynamical evolution of multiplanet systems on hot Jupiters (HJs), which are Jupiter-like planets that orbit their star in only a few days. They are thought to have formed at larger distances from the star, and must have migrated inwards. Here, we found that the long-term dynamical evolution in multiplanet systems can explain at most a few per cent of the observed HJs, unless the efficiency of tidal dissipation is much higher than is currently believed.